A guy on StackOverflow recently asked about unfunctional Parent control on Federated Experience Manager in Siecore 8.0. Here is his original question:

"I am trying to use Federated Experience Manager with an external
website. The static website has a JS beacon, so now I am able to open
external page with Experience Editor.

The issue happens when I try to add a placeholder to that external
static page (as per guide), parent dropbox do not present, so I am not
able to create a placeholder and any other operations FXM allows."

I have met that issue before, so was happy to share my experience:

I had that issue in past when tried to investigate Sitecore 8 new
features. I know it may sound weird, but this happens because your
license does not have FMX in it.

If you got you your license.xml file from previous sitecore versions,
then FXM would not be there, you need to request new license from
Sitecore that has this feature enabled.

Update: The good way to test that is to look beacon
file content (ex. in dev. tools) - if you do no have license beacon
would just have missing license text without any actual content. You may
check what you are actually licensed for from Sitecore menu (or
hamburger menu in 8.0+) from Content Editor, then selecting Licenses. If
you do not see something like Sitecore.Federated Experience (or similar
by sense) then you are definitely out of license for FXM.